1. Field
One embodiment of the invention relates to improvement of a video signal processing apparatus and video signal processing method, in which tone correction processing is provided to luminance signals based on the frequency obtained for each luminance level.
2. Description of the Related Art
As everyone knows, in recent years, flat-panel type large screen displays are developed and are put into practical use for color TV broadcast receivers etc. Now, in this kind of large-screen displays, in order to make displayed video images look clear, it is common practice to carry out tone correction processing for luminance components of video signals.
As this kind of tone correction processing for luminance components, a technique to correct tones in accordance with the frequency distribution of the luminance level of input video signals is known. The basic concept of this technique is to increase the gradient of the tone correction characteristic curve for the luminance level with large frequency and to decrease the gradient of the tone correction characteristic curve for the luminance level with small frequency.
By doing this, a dynamic range of a luminance level region occupying most of the input video signal is enlarged. As a result, the contrast feeling of video images is improved or correction is made to effectively express subtle tone differences.
Now, in the current basic tone correction processing means using the frequency of each luminance level, by cumulatively adding the frequency obtained at each luminance level from the low-order luminance level, luminance input/output conversion parameters, that is, a tone correction characteristic curve is prepared.
However, in this kind of tone correction processing means, in the event that information is locally concentrated to a specific luminance level, the luminance gradient of the concentrated portion becomes excessively steep, and conversely, in the portion with no information, the luminance gradient scarcely exists.
On the other hand, presently, it is considered to handle the frequency obtained at each luminance level by establishing limit values for the upper limit and the lower limit, respectively, but since this is a simple omission padding processing, the effects tend to be reduced for the original information.
In Jpn. Pat. Appln. KOKAI Publication No. 2005-86772, there is disclosed a configuration to automatically set a limit value of correction amount of each copy, prepare tone correction characteristics, and carry out tone correction in accordance with the luminance distribution of video image data read, but the correction amount limiting processing or the way to give the setting is complicated.